1. Field of the Invention
The present invention relates generally to nutrient additives for biological systems and more specifically to an additive for enhancing and prolonging mushroom growth and extending cropping, and to methods for producing such additive.
2. Description of the Prior Art
Millions of pounds of commercially produced, edible mushrooms, are grown and consumed annually in the United States. Commercial mushroom production is divided into several stages, with the first stage being the preparation of the media or compost upon which the mushrooms will grow. The compost is prepared by an aerobic fermentation process in outdoor piles at temperatures in excess of 165.degree. F. The compost is then subjected to an indoor pasturization process and cooled below 80.degree. F. At this point the compost is inoculated with mycelia which have been separately grown on a grain substrate such as rye or millet. This process is known as "spawning". The mycelia are allowed to colonize the compost for a two to three week period following the inoculation. Subsequently, the compost is covered with a thin layer of peat moss and a calcium carbonate buffer. This process is called "casing" and the peat moss layer is called the casing layer. Approximately twenty days after casing, the mushroom begins to produce the fruiting bodies or sporophores which are harvested and sold commercially as the edible mushrooms.
Because disturbing the spawn after it has been cased can have detrimental effects upon the production of fruiting bodies, the most advantageous time for the mushroom grower to add exogenous components to the compost is at the time of spawning, when such components may be freely admixed with the compost. However, it is not desiraable to have some types of materials, such as delayed release nutrients, biologically available until later in the crop (i.e. at the time of fruiting). Mushroom are grown in a series of crop cycles called "breaks" or "flushes". A typical mushroom compost preparation will produce three, four or five such flushes occuring at about one week intervals. However the latter flushes tend to produce lesser amounts and lower quality mushrooms.
The prior art has been directed toward the development and preparation of adjuvants intended primarily as delayed release nutrients to supply the mycelia with a good source prior to and during the first. An additional problem is present during the latter flushes which has not yet been addressed by the art. It is well-known tht the osmotic potential of the compost and casing layer increases during the later periods of the crop cycle, primarily during the third, fourth and fifth flush. The increase in osmotic potential is brought about by the secretion of metabolites and salts from the large biomass of mycelia growing in the casing layer and in the compost. As a response to this adverse biochemical environment, the mycelia cells synthesize ergosterol, a cholesterol-type compound tht is deposited in the cell membrane. Ergosterol synthesis has been noted in a paper by R. B. Holtz and D. E. Smith, presented at the proceeding of the Tenth International Congress of the Science and Cultivation of Edible Fungi, Part 1, 1979, page 437. The cell membrane, which is the primary regulator of metabolite transport into and out of the cell, becomes less permeable due to the ergosterol formation. This reduction of transport acts as a defense mechanism to protect the cell. However, reduced transport also means reduced mycelial activity and subsequently reduced production of mushroom fruiting bodies. Therefore, the yield of mushroom tissue declines both in quality and quantity in the later breaks because the mycelia cannot supply the expanding fruiting bodies with biochemical raw materials for cell synthesis and with water for cellular expansion.
It has been reported in the literature, for example, by Le Rudulier and R. C. Valentine, Trends in Biochemical Science, Volume 7, page 431, 1982, that some bacteria respond to increased osmotic stress by the production of osmoprotective compounds, betaine and glycyl-choline. The importance of this fact is that the organism must take up and/or synthesize osmoprotectant compounds such as at the time of osmotic stress. To provide these compounds prior to this time would not result in osmoprotectant activity, rather the compounds would enter other metabolic pathways and be used for other purposes.
Recent experiments with bacteria have shown that the addition of these osmoprotective compounds to in nutrient media can encourage growth even in situations where the salt content of the media exceeds the tolerance for normal growth. (See Le Rudulier, Strom, Dandekar, Smith and Valentine, Science, Volume 224, page 1064, 1984). Choline and betaine have been shown to protect cultures of E. coli against osmotic stress in high salt media. In higher plants, betaine has been shown to protect a root symbiont, Rhizobium meliloti as a free living organism and in the form of a nodulated seedling.
None of the prior art has however, shown that betaine and choline would have a similar effect in higher fungi, specifically Basidiomycetes. Furthermore, none of the prior art has applied the results of these studies toward the development of a functional osmoprotectant for fungi, which may be added to a commercial mushroom spawn and which would viably protect the later flushes against the effects of increased osmotic stress.